The specific aims of the proposal are to examine the effects of silica and Bacille Calmette - Guerin (BCG) on pulmonary cells and their immunocompetence. Silica and BCG will be administered separately and together by inhalation. The effects of these treatments will be determined by the following assays: antibody responses to antigens, alveolar macrophage phagocytic and bactericidal activity, alveolar macrophage cytotoxicity, production of chemotactic factors and production of macrophage ectoenzymes. In other experiments BCG treatments will be administered to previously silica-exposed mice in order to determine the proliferative response of cells to sensitizing antigen, the cellular immune response in footpads and lungs of sensitized animals and the proliferation and dissemination of viable BCG following aerosol injection. The studies should contribute to an increased knowledge of basic immunologic defense mechanisms in the lung as well as helping to explain the decreased resistance of silicotic individuals to infection with mycobacteria.